A modern vehicle headlamp assembly commonly includes sealed electrical connectors, sophisticated injection-molded lenses and molded, metal-coated reflectors which work in concert to collimate and distribute white light from an incandescent, halogen, or arc-discharge source (HID).
Many modern electric light sources are relatively inefficient, e.g., conventional tungsten incandescent lamps, or require high voltages to operate, e.g., fluorescent and arc-discharge lamps, and, therefore are not optimal for vehicular head lamp light sources where only limited power is available, only low voltage is available or where high voltage is unacceptable for safety reasons. Most conventional white-light headlamps rely upon incandescent, halogen or HID lamps as light sources. However, these lamps possess a number of shortcomings that must be taken into account when designing a headlamp assembly.
Incandescent lamps are fragile and have a short life even in stable environments and consequently must be replaced frequently at great inconvenience, hazard, and/or expense. In addition to their inherently short life, incandescent lamps are very susceptible to damage from mechanical shock and vibration. Automobiles experience severe shocks and significant vibration during driving conditions that can cause damage to incandescent lamps, particularly the filaments from which their light emissions originate.
Incandescent lights also exhibit certain electrical characteristics that make them inherently difficult to incorporate in vehicles, such as an automobile. For instance, when an incandescent light source is first energized by a voltage source, there is an initial surge of current that flows into the filament. This in-rush current, which is typically 12 to 20 times the normal operating current, limits the lifetime of the lamp, thus further amplifying the need for frequent replacement. Incandescent lamps also suffer from poor efficiency in converting electrical power into radiated visible white light. Most of the electrical energy they consume is wasted in the form of heat energy while less than 7% of the energy they consume is typically radiated as visible light.
Another problem associated with incandescent, halogen, and HID lamps is that they generate large amounts of heat for an equivalent amount of generated light. This results in very high bulb-wall temperatures and large heat accumulations which must be dissipated properly by radiation, convection, or conduction to prevent damage or destruction to the illuminator support members, enclosure, optics or to other nearby vehicle components. This high heat signature of common light sources in automotive headlamps has a particularly notable impact on the specialized reflector and lens designs and materials used to collimate and direct the light. Design efforts to dissipate the heat while retaining optical effectiveness further add requirements for space and weight to the illuminator assembly, a severe disadvantage for vehicular applications that are inherently sensitive to weight and space requirements.
Moreover, the illuminance of an incandescent light source depreciates over time. It is very common for a filament type light source used in headlamp applications to loose more than 25% of its output when compared to the initial output of the bulb. Very long life halogen bulbs may loose up to 50% of their output over their useful life.
HID lamps provide more light than that produced by halogen lamps and incandescent bulbs, and use less power than halogen, and thus, are more efficient. Moreover, since there is no filament to burn out, these bulbs are claimed to last for as much as 100,000 miles of driving time. However, although HID's last longer than halogen and incandescent light sources, they are very expensive and require the use of ballast. Moreover, a common complaint with HIDs is that they produce an excessive amount of glare. HID light sources (bulbs) typically have about two to three times the available light flux (volume) of halogen light sources and the HID beam pattern is more robust than that of halogen sources, providing more even and wider illumination and the potential for better visibility and comfort. This results in more light on the road surface and more of the roadway being illuminated. However, this additional light is not supposed to be projected upward from the lamp toward oncoming drivers' eyes. During inclement weather, when the road surface is wet, the additional volume of light can result in higher levels of light reflected off the road surface into other drivers' eyes.
More recently, great interest has been shown in the use of semi-conductor devices such as light emitting diodes (LEDs) as the light source for illuminator systems. Due to their strong coloration and relatively low luminous output as compared to incandescent lamps, early generations of LEDs found most of their utility as display devices, e.g., on/off and matrix-addressed indicators, etc. These uses still dominate the LED market today, however recent advances in LED materials, design and manufacturing have resulted in significant increases in LED luminous efficacy and, in their most recent commercial forms, exhibit a higher luminous efficacy than incandescent lights.
LEDs offer other many potential advantages as compared to other conventional low voltage light sources for vehicles. LEDs are highly shock resistant and therefore provide significant advantages over incandescent and fluorescent bulbs that can shatter when subjected to mechanical or thermal shock. LEDs possess operating lifetimes from 200,000 hours to 1,000,000 hours, as compared to the typical 1,000 to 2,000 hours for incandescent lamps, 1000 hours for halogen, and 5,000–10,000 hours for fluorescent bulbs. The heat generated by LED light sources is also significantly less than that generated by conventional vehicular headlamp light sources that use filaments. Since relatively little heat is generated by LED light sources, the volume inside the headlamp can be minimized, thereby minimizing package depth of the headlamp. Also, LED light sources have a very low level of light output degradation over time, i.e., less than ten percent over the life of the vehicle versus about twenty five percent of the life of the vehicle with conventional light sources.
Moreover, since conventional light sources generally utilize a single bulb or light source, headlamp design is generally limited. Use of an array of LED light source modules permit a range of possible headlamp design configurations. In addition, for customers who desire greater light output performance from the headlamp, more LED light source modules can be added. A further advantage of the use of an array of LED light source modules is the adjustability and adaptability of the headlamps utilizing such modules. By switching on or off certain LED modules within the headlamp, the beam pattern from the headlamp can be altered to meet road conditions or vehicle actions. For example, if some of the modules of the array are arranged to the right, when the vehicle enters a right turn, these modules can be selectively adjusted, either by switching them on or increasing their light output, to permit the driver of the vehicle greater visibility of the road and area into the right turn. Likewise, LED modules aimed to the left can be dimmed so as to minimize distraction to the driver. In addition, with an array of LED light source modules, failure of one or a couple of modules results only in a slight loss of light output as opposed to complete loss of light output resulting from the failure of conventional bulbs.
Finally, with LED headlamp arrays various individual lenses of the same or varying types can be associated with each individual LED to create different beam patterns and optimize those beam patterns depending on the desired use.
Thus, it is desirable to replace conventional bulbs with arrays of white light emitting diode light sources in headlamps used on vehicles. The present invention solves the above-identified problems associated with the use of conventional bulbs in vehicular headlamps.